1. Field of the Invention
The present invention relates to devices of the kind adapted to scan light on a pixel (picture element) by pixel basis in response to electronic address signals. More specifically, the present invention relates to improved light control devices and to electronic scanning and/or printing apparatus using such improved devices.
2. Description of the Prior Art
Recently, it has been found that light valve array devices provide a highly useful vehicle in electronic imaging. One preferred light valve configuration comprises a piece of ferro-electric ceramic material, such as lanthanum-doped lead zirconate titanate (PLZT), which is sandwiched between crossed polarizers and electrically activatible to operate in a Kerr cell mode. An array of such light valves comprises such crossed polarizers and a panel of PLZT material that has a plurality of electrodes formed on one of its major surfaces. The electrodes are arranged in a manner facilitating the selective application of discrete electrical fields across (in a direction perpendicular to the direction of viewing) discrete surface areas which constitute pixel portions of the panel. Upon application of such fields, the PLZT material becomes birefringent and rotates the direction of polarization of incident light by an extent dependent on the field magnitude. This results in transmission of light through the PLZT pixels and cooperating polarizers varying as a function of the respective addressing fields.
U.S. Pat. No. 4,229,095 discloses various embodiments of electronic color-imaging apparatus that utilize such light valve arrays to effect multicolor exposure of panchromatic recording media. For example, a color image is formed electronically by selectively opening and closing individual light valves of such arrays in synchronization with the energization of red, green and blue exposing sources and according, to the red, green and blue color information for the pixels of that image. One preferred embodiment disclosed in that patent comprises a linear light valve array disposed in spaced transverse relation to the recording media feed path. The pixels of the array are addressed concurrently with image information, a line at a time, and the movement of the recording medium, and the red, green and blue color exposures are synchronized with successive actuations of the linear array.
It can be appreciated that light valves must address many image pixels per line in order to form images having even moderate detail. The number of pixels per line increases in accordance with the resolution requirements of the imaging application, e.g. becoming as large as 200 pixels per inch or larger for high quality continuous tone imaging. Each pixel of the recording medium must be independently addressable with light in accordance with the unique content of the image to be reproduced. Therefore, discretely-activatible electrode means has been provided for each pixel portion of the light valve array, and each electrode means has had its own high voltage "off-on" switch, e.g. a transistor amplifier. The cost and complexity of these many switches and their connection and packaging present problems in electronic imaging with light valve devices.
Another problem encountered in fabricating light valve array devices relates to the electro-optic modulator panel, which is commonly formed as a linear strip having a length dimension sufficient to transverse an image exposure or scan zone. Although such linear modulator strips theoretically can be quite small in area (viz, the exposure zone length .times. one pixel in width), practical fabrication, handling and electronic packaging considerations militate toward a greater width. For example, while the width of the strip could be on the order of 0.1 mm from an optical viewpoint, difficulties are presented in fabricating and handling modulator strips less than 10 mm in width. Thus, there is a "waste" of modulator material, which is expensive.
Still another problem exists with respect to such linear light valve array configurations. Specifically, the magnitude of their length usually necessitates special illuminating and imaging optics, which further adds to the cost of using such devices.